Aortic root dilation is one of the most common causes of aortic valve incompetence in North America. Prevalence of surgical corrections for this pathology has increased considerably during the last two decades. Mechanisms involved in this pathology have been experimentally and clinically studied resulting in a variety of surgical corrections. While some of the surgical corrections are better adapted to the aortic physiology, others, less convenient, have been associated with recurrent aortic disease and valvular insufficiency. There is room for improvement in providing a surgical correction that respects the normal aortic root physiology in the correction of aortic valve insufficiency associated to aortic annulo-ectasia, aortic aneurysm and other such dilatations.
As is well known, the mammalian heart is an organ made up of four muscular chambers that function together to pump blood throughout the body. Each of the four chambers has an associated downstream one-way valve made up of movable, coapting leaflets or cusps which cooperate to prevent the backward flow of blood, or regurgitation, into their respective chambers. Two such heart valves, the aortic and pulmonary valves, also commonly known as the semilunar valves, are characterized by three leaflets or cusps. The aortic valve leaflets are attached within the aortic root, to a tri-scalloped or triple scalloped line of collagenous, fibrous tissue generally referred to as the valve annulus. As such, a three-pointed crown-like structure serves to support the aortic valve cusps or leaflets. The U-shaped convex lower edges of each leaflet are attached to, and suspended from, the base of the aortic root, with the upper free edges or margins of each leaflet being free to move and project into the lumen of the aorta. Two adjacent leaflets approach one another at one of the three points of said crown-like structure to define a commissure of the aortic valve. Behind each leaflet, the aortic vessel wall bulges outward, forming a pouch-like dilatation known as the sinus of Valsalva. In the region located slightly above the level of the commissures, the aortic root creating the sinuses of Valsalva merges into the substantially tubular portion of the ascending aorta at a substantially planar transition zone commonly known as the sinotubular junction (STJ). The aortic root houses the aortic valve structure and generally includes the portion of the native aortic conduit extending form the left ventricular outflow tract (LVOT) to the portion of ascending aorta (AA) slightly above the sinotubular junction. Typically, aortic root reconstructions or interventions usually involve the aortic valve, while ascending aorta interventions usually exclude the aortic valve and involve the native aortic conduit located generally downstream of the sinotubular junction.
During ventricular systole, the leaflets are passively thrust upward and outwardly away from the centre of the aortic lumen, while in a synchronous manner, the commissures move out radially with the aortic root. As such, the free edges of the leaflets are no longer in contact with each other as they assume a triangular geometric relationship when viewed along the axis of the aortic lumen. This may also be referred to as triangulation of the valve leaflets (FIG. 2C). During ventricular diastole, the leaflets fall passively into the lumen of the aorta, and coapt at their respective free edges to support the column of blood above. In a synchronous manner, the commissures move radially inward with the aortic root, thereby allowing the free edges to resume contact with each other and assume a Y-shaped geometric relationship (FIG. 2B). This may also be referred to as coaptation of the valve leaflets. In a healthy aortic valve, the geometry of the leaflets and the strong fibrous tissue support thereof provide excellent approximations of the leaflets and prevent regurgitation of flow through the aortic valve. In a diseased aorta, the dilatation of the aortic root or valve annulus, or the aneurysm of the aortic wall, results in compromised leaflet coaptation leading to regurgitation and valve insufficiency.
The aortic valve is a critical component in maintaining adequate flow of oxygenated blood to the rest of the body. The conduit downstream of the aortic valve, generally above the sinotubular junction, is known as the ascending aorta. A number of diseases lead to dilatation of the aortic root structure and aortic valve annulus, also called aneurysm or ectasia, which in turn affects the ability of the aortic valve leaflets to coapt or close completely. This ensuing condition, known as aortic insufficiency, can severely diminish the heart's ability to effectively deliver blood to the rest of the body or to the heart muscle, and can lead to serious complications and death.
Until the early 1990s, a common treatment for managing aortic insufficiency caused by aortic root dilatation consisted of completely resecting the aortic valve and aortic root, and replacing such native structures with a composite heart valve—aortic root prosthesis (i.e. an aortic valved conduit). One of the drawbacks of this surgical intervention, known as the Bentall procedure, is that in patients having relatively healthy leaflets, such leaflets are sacrificed and replaced by a prosthetic valve in order to correct the aortic dilatation. In addition, there is a need for prolonged anti-coagulation therapy in the case of Bentall procedures using mechanical heart valves, and a risk of valve degradation and reoperation in the case of Bentall procedures using bioprosthetic heart valves.
Some of the problems associated with a Bentall procedure have been addressed through the development of a surgical procedure known as aortic valve-sparing, in which the aortic root is resected above the aortic annulus, leaving a scalloped portion of native tissue, or fringe, extending slightly above the leaflets. From approximately the same starting point, two valve-sparing procedures have evolved. The first, known as reimplantation (FIG. 26A), involves the placement of a Dacron root prosthesis or synthetic aortic conduit over the scalloped native tissue, where it is sutured both below the valve leaflets through the valve annulus, and above the valve leaflets. The procedure is generally long and difficult to perform, and often results in leaflet impact or concussion with the walls of the Dacron prosthesis during the ejection phase of the cardiac cycle. In addition, the absence of radial compliance of the Dacron root prosthesis does not allow for an increase in diameter at the sinotubular junction STJ during ejection, which is an important aspect in providing optimal blood transport while preserving valve dynamics and valve leaflet durability. As such, the normal valve physiology is compromised in this valve-sparing intervention.
The second type of valve sparing operation, known as remodelling (FIG. 26B), involves scalloping the Dacron root prosthesis to essentially match the remaining native tissue, and using a running suture to attach the prosthesis to the native aortic root tissue. Although this method addresses some of the problems of the reimplantation method, it does not directly constrain the valve annulus diameter, which has been seen to result in annular dilatation over time. As such, this procedure is not well suited for resizing a dilated valve annulus, and may be limited to replacing aneurysmal aortic tissue. Since it also relies on a Dacron vascular conduit, which is radially non-expansible, the expansion of the aortic root at level of commissures, in the plane joining the commissures or scalloped peaks of native tissue, tends to be constrained by the conduit fabric hoop. As such, the leaflet free edges are hindered in assuming their triangulated relationship, since the plane containing the STJ is generally not expansible in this surgical procedure. Unlike the reimplantation procedure, however, the leaflets have a lower likelihood of hitting the conduit wall since pseudo-sinuses may be fashioned from a scalloped Dacron conduit to recreate the pouch-like configuration seen in a healthy aortic root. Nonetheless, in the remodelling valve-sparing intervention, the normal native valve physiology is compromised, and the effectiveness of resizing a dilated aortic annulus, or preventing its future dilatation, with a scalloped vascular conduit remains questionable.
Although useful and widely accepted for some aortic reconstruction procedures, conventional valve-sparing procedures and devices nevertheless suffer from numerous drawbacks or shortcomings that are manifested and become apparent both during the operative and post-operative periods.
Accordingly, there exists a need for an improved aortic root reconstruction procedure, and enabling devices, that allows correction of a dilated aortic annulus, or replacement of aneurysmal aortic tissue, while preserving the native leaflets and maintaining normal valve physiology. Typical prior art devices and methods for aortic reconstruction or valve sparing interventions do not offer a dynamic device configuration that may advantageously vary during the different phases of the cardiac cycle, and consequently restore or preserve normal aortic valve physiology. More specifically, there exists a need for such an aortic reconstruction device which, when implanted, dynamically controls the valve annulus both at the level of the aortic root base, and at the level of the valve commissures, thereby leading to optimal blood flow conditions therethrough and leaflet durability. Also beneficial would be a procedure with reduced time and difficulty relative to current valve sparing procedures.